Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias, with an abnormally rapid rhythm being referred to as a tachycardia. The present invention is concerned with the treatment of tachycardia that are frequently caused by the presence of an "arrhythmogenic region" or "accessory atrioventricular pathway" close to the inner surface of the heart chambers. The heart includes a number of normal pathways that are responsible for the propagation of electrical signals from the upper to the lower chambers necessary for performing normal systole and diastole function. The presence of arrhythmogenic region or accessory pathway can bypass or short circuit the normal pathways, potentially resulting in very rapid heart contractions, referred to here as tachycardia.
Treatment of tachycardias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying causes Implantable devices only correct the arrhythmia after it occurs. Surgical and catheter-based treatments, in contrast, will actually cure the problem, usually by ablating the abnormal arrhythmogenic tissue or accessory pathway responsible for the tachycardia. It is important for a physician to accurately steer the catheter to an exact site for ablation. Once at the site, it is important for a physician to control the emission of energy to ablate the tissue within a heart.
Of particular interest to the present invention are radiofrequency (RF) ablation protocols that have been proven to be highly effective in tachycardia treatment while exposing a patient to minimal side effects and risks. Radiofrequency catheter ablation is generally performed after conducting an initial mapping study where the locations of the arrhythmogenic region and/or accessory pathway are determined. After a mapping study, an ablation catheter is usually introduced to the target heart chamber and is manipulated so that the tip electrode lies exactly at the target tissue sites. Radiofrequency energy or other suitable energy is then applied through the tip electrode to the cardiac tissues in order to ablate the tissue of arrhythmogenic site or the accessory pathway. By successfully destroying that tissue, the abnormal signal patterns responsible for the tachycardia may be eliminated. However, in the case of atrial fibrillation (AFib), multiple arrhythmogenic sites and/or multiple accessory pathways exist. The conventional catheter with a single ablation tip electrode can not effectively cure the symptoms. In the paroxysmal AFib, the origin of the arrhythmia may lie near the ostium of the pulmonary vein. A complete circular lesion is required around the ostium to cure the arrhythmia.
Atrial fibrillation is believed to be the result of the simultaneous occurrence of multiple wavelets of functional re-entry of electrical impulses within the atria, resulting in a condition in which the transmission of electrical activity becomes so disorganized that the atria contracts irregularly. Once considered a benign disorder, AFib now is widely recognized as the cause of significant morbidity and mortality. The most dangerous outcome from AFib is thromboembolism and stroke risk, the latter due to the chaotic contractions of the atria causing blood to pool. This in turn can lead to clot formation and the potential for an embolic stroke. According to data from the American Heart Association, about 75,000 strokes per year are AFib-related.
A catheter utilized in the endocardial RF ablation is inserted into a major vein or artery, usually in the neck or groin area. For paroxysmal AFib indications, a catheter is approached from the atrium to the ostium of a pulmonary vein. The tip section of a catheter is referred to here as the portion of that catheter shaft containing the electrode means which may be deflectable and may be adapted to form a circular or an irregular-shape complete loop lesion. The electrode means is to be positioned against the ostium of the pulmonary vein, whereby the circular electrode means having a firm support, such as an inflated balloon, can be pressed against the tissue for ablation.
Several patents disclose the use of a guiding introducer to guide the ablation catheter into the place. Examples as U.S. Pat. No. 5,840,027 to Swartz et al., U.S. Pat. No. 5,833,673 to Ockuly et al., U.S. Pat. No. 5,814,029 to Hassett, U.S. Pat. No. 5,814,017 to Hassett et al., U.S. Pat. No. 5,800,413 to Swartz et al., and U.S. Pat. No. 5,725,512 to Swartz et al. However, none of the above-referred patents disclose a self-guiding catheter for ablation of tissues. U.S. Pat. No. 5,840,076 discloses a balloon type electrode catheter by using balloon as a medium to create a circular lesion, wherein the balloon is made of a porous material. Said patent discloses a RF circuit by including a patient in the circuit loop, whereby the heat generated by the RF current at the tissue contact site may unexpectedly hurt the patient. The local heat source may make the temperature of the heated balloon non-uniformly around the balloon.
There is an urgent clinical need to have a self-guiding catheter that can provide a uniformly heated balloon for creating a circular lesion. The temperature of the uniformly heated balloon can be controlled by a temperature sensor and a temperature controller without inducing blood coagulation during ablation operations.